1. Field of the Invention
This invention relates to a nonvolatile semiconductor memory.
2. Description of the Related Art
To write “0” data into a NAND flash memory, it is necessary to make a sufficient potential difference between a channel formed between the source and drain and a control gate and inject charges into a charge storage layer.
To write “1” data, however, a specific potential is applied to the channel in advance to prevent a potential difference from being made between the control gate and channel, thereby preventing charges from being injected into the charge storage layer.
Actually, even in a memory cell into which “1” data is to be written, there is a potential difference between the control gate and channel, allowing a small number of charges to be injected into the charge storage layer (hereinafter, this phenomenon is referred to as program disturbance). Jpn. Pat. Appln. KOKAI Publication No. 2000-149566 has disclosed the problem of deterioration in the operational reliability of a NAND flash memory.